1. Field of the Invention
This invention relates to a process for conversion of feedstock comprising C.sub.2.sup.+ olefins, C.sub.2 -C.sub.7 paraffins or mixtures thereof to product comprising C.sub.5.sup.+ hydrocarbons. The process comprises contacting, under conversion conditions, said feedstock with a catalyst comprising a siliceous zeolite having been prepared by the method comprising providing a boron-containing zeolite Beta, treating the zeolite with silicon tetrachloride at a temperature and for a time sufficient to replace boron with silicon, and recovering the siliceous zeolite having reduced boron content but preserved initial aluminum content.
2. Description of Prior Art
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversions. Certain zeolitic materials are ordered, porous crystalline silicates having a definite crystalline structure within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties.
Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline silicates. These silicates can be described as a rigid three-dimensional framework of SiO.sub.4 and AlO.sub.4 in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total non-silicon lattice element, e.g. aluminum, and silicon atoms to oxygen is 1:2. the electrovalence of the tetrahedra containing, for example, aluminum is balanced by the inclusion in the crystal of a cation, for example, an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of the non-silicon lattice element, e.g. aluminum, to the number of various cations, such as Ca/2, Sr/2, Na, K or Li is equal to unity. One type of cation may be exchanged either entirely or partially by another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given crystalline silicate by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
Prior art techniques have resulted in the formation of a great variety of synthetic crystalline silicates. These silicates have come to be designated by convenient symbols, as illustrated by zeolite ZSM-5 (U.S. Pat. No. 3,702,886).
The use of certain zeolites as catalyst components is taught in U.S. Pat. No. 4,305,808, for example.
The silica-to-alumina ratio of a given zeolite is often variable; for example, zeolite X (U.S. Pat. No. 2,882,244) can be synthesized with a silica-to-aluminum ratio of from 2 to 3; zeolite Y (U.S. Pat. No. 3,130,007) from 3 to about 6. In some zeolites, the upper limit of silica-to-alumina ratio is virtually unbounded. Zeolite ZSM-5 is one such material wherein the silica-to-alumina ratio is at least 5. U.S. Pat. No. 3,941,871 discloses a crystalline metal organo silicate essentially free of aluminum and exhibiting an X-ray diffraction pattern characteristic of ZSM-5. U.S. Pat. Nos. 4,061,724; 4,073,865 and 4,104,294 describe microporous crystalline silicas or organo silicates wherein the aluminum content present is at impurity levels. Zeolite Beta is described in U.S. Pat. No. 3,308,069, the contents of which are entirely incorporated herein by reference.
U.S. Pat. Nos. 3,960,978 and 4,021,502, disclose conversion of C.sub.2 -C.sub.5 olefins, alone or in admixture with paraffinic components, into higher hydrocarbons over crystalline zeolites having controlled acidity. U.S. Pat. Nos. 4,150,062, 4,211,640 and 4,227,992 teach processing techniques for conversion of olefins to gasoline and distillate. U.S. Pat. No. 4,504,691 teaches a multi-step process for converting olefinic feedstock comprising ethylene and C.sub.3.sup.+ olefins to heavier liquid hydrocarbon product. The above identified disclosures are incorporated herein by reference.
U.S. Pat. No. 3,760,024 claims a process for producing aromatic compounds from C.sub.2 -C.sub.4 paraffins, olefins or mixtures thereof. U.S. Pat. No. 3,827,968 claims a process for conversion of C.sub.5.sup.- olefin-containing gas to product comprising aromatics. U.S. Pat. No. 4,120,910 claims a process for converting a gaseous paraffinic hydrocarbon feedstock containing ethane to aromatic compounds. U.S. Pat. No. 4,157,293 claims a process for converting C.sub.2 -C.sub.10 hydrocarbons consisting essentially of paraffins, olefins or their mixtures over a catalyst comprising a zeolite having a SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of at least 12, a Constraint Index of 1 to 12 and containing zinc and another named metal. U.S. Pat. No. 4,465,884, teaches conversion of C.sub.3.sup.+ olefins to higher molecular weight product comprising non-aromatics over catalyst comprising, for example, zeolite Beta having a silica/alumina mole ratio greater than 100.
Olefinic feedstocks may be obtained from various sources, including fossil fuel processing streams, such as gas separation units, cracking of C.sub.2.sup.+ hydrocarbons, coal byproducts, and various synthetic fuel processing streams. Cracking of ethane and conversion of conversion effluent is disclosed in U.S. Pat. No. 4,100,218 and conversion of ethane to aromatics over Ga-ZSM-5 is disclosed in U.S. Pat. No. 4,350,835. Olefinic effluent from fluidized catalytic cracking of gas oil or the like is a valuable source of olefins, mainly C.sub.3 -C.sub.4 olefins.